Kang Daniel G, Wagner Scott C, Tracey Robert W, Cody John P, Gaume Rachel E, Lehman Ronald A
Madigan Army Medical Center, Tacoma, WA, USA.
Walter Reed National Military Medical Center, Bethesda, MD, USA.
Global Spine J. 2017 Oct;7(7):681-688. doi: 10.1177/2192568217700105. Epub 2017 May 31.
In vitro human cadaveric biomechanical analysis.
To evaluate the segmental stability of a stand-alone spacer (SAS) device compared with the traditional anterior cervical plate (ACP) construct in the setting of a 2-level cervical fusion construct or as a hybrid construct adjacent to a previous 1-level ACP construct.
Twelve human cadaveric cervical spines (C2-T1) were nondestructively tested with a custom 6-degree-of-freedom spine simulator under axial rotation (AR), flexion-extension (FE), and lateral bending (LB) at 1.5 N m loads. After intact analysis, each specimen underwent instrumentation and testing in the following 3 configurations, with each specimen randomized to the order of construct: (A) C5-7 SAS; (B) C5-6 ACP, and C6-7 SAS (hybrid); (C) C5-7 ACP. Full range of motion (ROM) data at C5-C7 was obtained and analyzed by each loading modality utilizing mean comparisons with repeated measures analysis of variance with Sidak correction for multiple comparisons.
Compared with the intact specimen, all tested constructs had significantly increased segmental stability at C5-C7 in AR and FE ROM, with no difference in LB ROM. At C5-C6, all test constructs again had increased segmental stability in FE ROM compared with intact (10.9° ± 4.4° Intact vs SAS 6.6° ± 3.2°, < .001; vs.Hybrid 2.9° ± 2.0°, = .005; vs ACP 2.1° ± 1.4°, < .001), but had no difference in AR and LB ROM. Analysis of C6-C7 ROM demonstrated all test groups had significantly greater segmental stability in FE ROM compared with intact (9.6° ± 2.7° Intact vs SAS 5.0° ± 3.0°, = .018; vs Hybrid 5.0° ± 2.7°, = .018; vs ACP 4.4° ± 5.2°, = .005). Only the hybrid and 2-level ACP constructs had increased stability at C6-C7 in AR ROM compared with intact, with no difference for all test groups in LB ROM. Comparison between test constructs demonstrated no difference in C5-C7 and C6-C7 segmental stability in all planes of motion. However, at C5-C6 comparison between test constructs found the 2-level SAS had significantly less segmental stability compared to the hybrid (6.6° ± 3.2° vs 2.9° ± 2.0°, = .025) and ACP (6.6° ± 3.2° vs 2.1° ± 1.4°, = .004).
Our study found the currently tested SAS device may be a reasonable option as part of a 2-level hybrid construct, when used below an adjacent 1-level ACP, but should be used with careful consideration as a 2-level SAS construct. Consequences of decreased segmental stability in FE are unknown; however, optimal immediate fixation stability is an important surgical principle to avoid loss of fixation, segmental kyphosis, interbody graft subsidence, and pseudarthrosis.
体外人体尸体生物力学分析。
在双节段颈椎融合结构或作为与先前单节段前路颈椎钢板（ACP）结构相邻的混合结构的情况下，评估独立间隔器（SAS）装置与传统前路颈椎钢板（ACP）结构的节段稳定性。
使用定制的六自由度脊柱模拟器，在1.5 N·m载荷下，对12具人体尸体颈椎（C2-T1）进行轴向旋转（AR）、屈伸（FE）和侧弯（LB）的无损测试。在完整分析之后，每个标本以以下3种配置进行器械植入和测试，每个标本随机分配构建顺序：（A）C5-7 SAS；（B）C5-6 ACP和C6-7 SAS（混合）；（C）C5-7 ACP。通过每种加载方式获得C5-C7的全范围运动（ROM）数据，并利用均值比较和重复测量方差分析以及Sidak校正进行多重比较来分析。
与完整标本相比，所有测试结构在AR和FE ROM中C5-C7节段稳定性均显著增加，LB ROM无差异。在C5-C6，与完整标本相比，所有测试结构在FE ROM中节段稳定性再次增加（完整标本10.9°±4.4°，SAS为6.6°±3.2°，P<0.001；混合结构为2.9°±2.0°，P = 0.005；ACP为2.1°±1.4°，P<0.001），但在AR和LB ROM中无差异。C6-C7 ROM分析表明，与完整标本相比所有测试组在FE ROM中节段稳定性显著更高（完整标本9.6°±2.7°，SAS为5.0°±3.0°，P = 0.018；混合结构为5.0°±2.7°，P = 0.018；ACP为4.4°±5.2°，P = 0.005）。仅混合结构和双节段ACP结构在AR ROM中C6-C7的稳定性比完整标本增加，所有测试组在LB ROM中无差异。测试结构之间的比较表明，在所有运动平面中C5-C7和C6-C7节段稳定性无差异。然而，在C5-C6测试结构之间的比较发现，双节段SAS与混合结构（6.6°±3.2°对2.9°±2.0°，P = 0.025）和ACP（6.6°±3.2°对2.1°±1.4°，P = 0.004）相比节段稳定性显著更低。
我们的研究发现，当前测试的SAS装置作为双节段混合结构的一部分（当用于相邻单节段ACP下方时）可能是一个合理的选择，但作为双节段SAS结构使用时应谨慎考虑。FE中节段稳定性降低的后果尚不清楚；然而，最佳的即刻固定稳定性是避免固定失败、节段后凸、椎间融合器下沉和假关节形成的重要手术原则。
